One of the problems inherent in any type of lightweight, low power vehicle such as a bicycle is a high ratio of aerodynamic drag to power output. A bicycle being ridden at 30 mph has about 90% of it's power used to push air out of the way. Trying to overcome this problem has led to the development of many types of low frontal area velocipedes that reduce aerodynamic drag but have many new problems associated with them. Some of these problems are large turning radius, poor cornering, poor braking, wide track, long wheelbase, heavy construction, and dynamic instability. These problems cause difficulties using the vehicles in traffic, parking, maneuvering, or operating on hilly terrain or at high speeds, therefore, present designs have shown little overall advantage over conventional bicycles.
In order to overcome these problems a vehicle is needed which provides narrow overall width, short wheelbase, high cornering speeds with a small turning circle, and light, stable configuration. A common design locates a pair of steered wheels at the front of a vehicle and one or two driven wheels at the rear with a supine or recumbent rider located in-between. This design exhibits a conflict between narrow track and hard cornering ability and also a complex trade-off between turning radius, wheelbase length, track width, and construction weight. A differing and uncommon design, possibly better able to meet these critera, is a tricycle design wherein the rider is in a recumbent position. A front wheel, driven but unsteered, is located between his feet, and a pair of steered rear wheels are located below and behind the rider. Hard cornering can be attained while still retaining a narrow track by allowing the rider to lean "into" the corner. A small turning circle is attained both by the short wheelbase and the ability to have the steered wheels turn a sharp angle.
Assorted vehicle designs that utilize the tipping and rear steering approach have been developed. Altorfer, U.S. Pat. No. 3,746,118 shows a vehicle with improved cornering due to a shifted center of gravity caused by tipping the rider and part of the vehicle. Rich, U.S. Pat. No. 3,669,468 takes this a step further with a front drive, rear steered tricycle that tips proportionately with the steering angle and is meant as a low speed child's toy.
A more advanced design is disclosed by Hopkins, U.S. Pat. No. 4,198,072. This design incorporates a driven front wheel that does not steer, but which does tip with the frame and rider to change the center of gravity, a pair of steered rear wheels, and the rider in a recumbent position. Hopkins uses a solid, transverse, steered rear axle with a small wheel on each end and a linkage which forces the frame to tip proportionately to the steering angle, similar to Rich, but with an additional control movement that alters the proportion in such a way that the rider can choose the ratio of tipping to steering that he judges necessary for his speed.
My new method differs by using an improved rear geometry that allows any wheel size to be used and greatly improves the stability at speed by reacting to the dynamic forces caused by cornering, speed, gravity, and road surface. The means to control tipping and steering also have no mechanical connection between them in order that the improved stability can be utilized.